1. Field of the Invention
The present invention relates to a ceramic composition for use in a ceramic circuit board having an integrated circuit mounted thereon and the circuit board, more particularly to a ceramic composition capable of being sintered at a low temperature, lower than 1,000.degree. C., and a multilayered ceramic circuit board produced by sintering a conducting layer and an insulating layer together. The ceramic circuit board is used for an electronic device, particularly an electronic computer.
2. Description of Related Art
Hitherto there has been mainly used alumina, Al.sub.2 O.sub.3, for a multilayered circuit board, which has a silicon semiconductor integrated circuit element, and a high-melting point metal such as molybdenum, Mo, or tungsten, W, as a conducting material capable of being sintered together with alumina. However, since alumina has a coefficient of thermal expansion as high as about 7.times.10.sup.-6 /.degree.C., the conducting connection between an alumina board and a silicon semiconductor element undergoes a large amount of stress, when the board and the element are connected directly to each other. For this reason prior multilayered circuit boards are not reliable. Furthermore, since alumina has a relatively higher relative permittivity of about 10, the signal propagation speed thereof is not satisfied. In addition, the abovementioned high-melting point metal has a relatively high resistance. In order to solve such problems, Japanese Patent Kokoku (Post-Exam. Publn.) No. 2-49550 and Japanese Patent Kokai (Laid-Open) No. 63-40397 proposed to substitute for alumina a glass ceramic as insulating material, which is able to be sintered at a temperature of not higher than 1,010.degree. C. and has a relative permittivity of 6 or less and a coefficient of thermal expansion near that of silicon and, for the high-melting point metal as conducting material, copper having a lower resistance than that of the high-melting point metal.
In order to improve the performance and reliability of the ceramic circuit board for mounting the silicon semiconductor integrated circuit element thereon, the ceramics for the board are required (1) to be able to be sintered at a temperature of not higher than 1,000.degree. C., preferably 850.degree. to 950.degree. C. and (2) have a low relative permittivity of less than 6.0, preferably 5.0, (3) a coefficient of thermal expansion near that of silicon, i.e., (3.1.+-.1.0).times.10.sup.-6 /.degree.C., and (4) a higher bending strength.